[ECOS] Guidance on ROMRAM ldi

[Michael Bergandi <mbergandi at gmail dot com>]

Hi all,

I am trying to learn more about the linker file used in a ROMRAM
configuration. I have looked at several other ROMRAM ldi files for the
ARM, but I can't seem to find much agreement as to the proper way to
set up the SECTIONS section.

Our board has 2MB ROM and 32MB RAM and uses an iMX27 (ARM9) processor.
The current ldi file is adapted from a Freescale Redboot port to the
iMX27 LiteKit and looks like this:

MEMORY
{
    ram : ORIGIN = 0, LENGTH = 0x02000000
    rom : ORIGIN = 0xA1E00000, LENGTH = 0x00200000
}

SECTIONS
{
    SECTIONS_BEGIN
    SECTION_rom_vectors (rom, 0xA1E00000, LMA_EQ_VMA)
    SECTION_text (rom, ALIGN (0x4), LMA_EQ_VMA)
    SECTION_fini (rom, ALIGN (0x4), LMA_EQ_VMA)
    SECTION_rodata (rom, ALIGN (0x4), LMA_EQ_VMA)
    SECTION_rodata1 (rom, ALIGN (0x4), LMA_EQ_VMA)
    SECTION_fixup (rom, ALIGN (0x4), LMA_EQ_VMA)
    SECTION_gcc_except_table (rom, ALIGN (0x4), LMA_EQ_VMA)
    SECTION_fixed_vectors (ram, 0x20, LMA_EQ_VMA)
    SECTION_sram (ram, 0x8000, FOLLOWING (.gcc_except_table))
    SECTION_data (ram, ALIGN (0x4), LMA_EQ_VMA)
    SECTION_bss (ram, ALIGN (0x4), LMA_EQ_VMA)
    CYG_LABEL_DEFN(__heap1) = ALIGN (0x8);
    SECTIONS_END
}

If I understand correctly, the lengths provided from rom and ram in
the MEMORY section should be the actual size without concession for a
copy of ROM that would consume a portion of the RAM.

The rom ORIGIN is an offset into the RAM (which is mapped to both
0x00000000 and 0xA0000000). We want our app to be loaded to the end of
the RAM.

In some of the other ROMRAM ldi files I looked at, the SECTION
declarations use only 'ram' and not 'rom'. I'm thinking this may not
matter depending on the order and SECTION declaration options
(assuming you are only working with a single chunk off RAM). Is this
thinking correct?

I have also seen some discussion in the archives suggesting that using
LMA_EQ_VMA is not the right thing to use. Is there  a final word on
this? Should I use only FOLLOWING, as I have seen elsewhere?

Is there some general rules of thumb on setting up the SECTION
declarations to avoid common mistakes/problems?

Any advice is welcome.

Thank you,

-- 
Michael Bergandi

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